IIT JEE Entrance Exam> Next number 2, 5, 11, 20, 32, 47?...

Next number 2, 5, 11, 20, 32, 47?

TEJKIRAT SINGH , 9 Years ago

Grade 12th pass

3 Answers

Vikas TU

Last Activity: 9 Years ago

Yeah absolutely keep adding the multiples of 3 in your given series.
3+2=5
6+5=11
9+11=20
12+20=23
15+32=47
18+47=65
So the next number will 65.

Approved

Vikas TU

Last Activity: 9 Years ago

second method:

Series 2, 5, 11, 20, 32, 47
Find = next number
In this series each digit has the difference of 3,6,9,12,15 etc..
so next series will have the difference of 18.
It means next number will be 47+18 = 65.

Vikas TU

Last Activity: 9 Years ago

3^rd on1:

Solution:

i) t₂ - t₁ = 5 - 2 = 3
t₃ - t₂ = 6
t₄ - t₃ = 9 and so on...
So let the nth term - (n-1)th term be = x.

ii) Sum of all the above = nth term - t₁ = 3 + 6 + 9 + ----- [This is in AP, whose first term = 3 and common difference = 3 and number of terms = (n - 1); the sum of which = [(n - 1)/2}*[2*3 - {(n - 1) - 1}*3] = 3n(n - 1)/2]

Thus nth term - t₁ = 3n(n - 1)/2
==> nth term = 3n(n - 1)/2 + 2 = (3n² - 3n + 4)/2

As you require 7th term, n = 7
Substituting the same in the above, 7th term = (3*7² - 3*7 + 4)/2 = 130/2 = 65